docs: add changelog for v0.2.1

Author: windvex

CHANGELOG.md

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+# Changelog
+All notable changes to this project will be documented in this file.
+
+The format follows [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),  
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+---
+
+## [0.2.1] - 2025-10-14
+### Added
+- **PeerJS standalone defaults**
+  - Built-in configuration compatible with Wind’s production signaling service:
+    - `host=core.windcrypto.com`
+    - `port=443`
+    - `secure=true`
+    - `path='/'`
+    - `key='peerjs'`
+- **Server configuration helpers**
+  - `configureForCore()` – instantly configure connection for Wind’s main backend.
+  - `setServer()`, `setPath()`, `setKey()`, `setSecure()`, and `setPort()` for granular overrides.
+- **ICE / TURN utilities**
+  - `addIceServer()`, `setIceServers()`, and `clearIceServers()` for dynamic WebRTC setups.
+  - Automatic TURN validation to prevent missing credentials (`username` / `credential`).
+- **Event system**
+  - Re-emits PeerJS events: `open`, `close`, `disconnected`, `error`, and `session`.
+- **Session persistence**
+  - Automatically reuses valid sessions via `sessionStorage` (with `exp` and `sig`).
+
+### Changed
+- TypeScript refactor and dual-build system (ESM + CJS + Type definitions).
+- Re-login logic now restores wallet session if still valid.
+- Improved error handling and event propagation.
+
+### Fixed
+- Prevented WebRTC error: “Both username and credential are required when the URL scheme is turn/turns.”
+- Cleared expired sessions from storage automatically.
+- Improved decoding and validation of `IdentityProof` objects.
+
+---
+
+## [0.1.1] - 2025-08-12
+### Added
+- **Initial public release of WindKit.**
+  - A protocol for connecting Vexanium DApps to the Wind wallet.
+- Core features:
+  - Cross-device login via VSR (Vexanium Signing Request).
+  - Transaction signing (single or multiple actions).
+  - Message signing.
+  - Shared secret (ECDH) encryption.
+  - PeerJS-based WebRTC signaling.
+- Published package: [`windkit`](https://www.npmjs.com/package/windkit).
+
+---
+
+### 🧩 Links
+- **Repository:** [https://github.com/windvex/windkit](https://github.com/windvex/windkit)
+- **npm:** [https://www.npmjs.com/package/windkit](https://www.npmjs.com/package/windkit)
+- **License:** [MIT](./LICENSE)